I have written this before in a different topic, but I think it was out of place so I decided to copy it down in this thread.

Zlythax. (Poison/Dark)
I thought it was a cool name, it's design sorta looks like a cross between the creature 'venom' from spiderman, and sableye. This creature has a long, furry tongue that hangs out from it's Sableye - like grin. It has blank, soulless blue eyes (like Sylveon), and has long, black scythes that replace it's hands (like Kabutops's blades - except longer and black).
Now it's stats:

Ability: Assassin (Increases the accuracy of OHKO moves, like guillotine, from 30% to 80%)

Hp: 100
Atk: 15
Def: 80
SpAtk: 15
SpDef: 80
Spd: 150

Base stat total: 440

You are probably disappointed with it's attack stats, but when it has the ability 'Assassin', who needs attack? Zlythax can learn ALL the OHKO moves, including a new one called 'Death Slice', a dark type guillotine which is it's signature move.
Since Zlythax has a stunning 150 speed stat, it should OHKO everything in it's path, at least 80% of the time!

That is so ridiculously overpowered that it's definitely never going to happen. If something like this learned Hone Claws, it's OHKO moves would hit 100% of the time. The design is a nice enough concept, but that kind of ability with that speed stat is not going to happen. If you threw a Choice Scarf on it it would be unbeatable outside of extremely lucky misses and if something got the chance to either hit it with a Choice Banded Earthquake or got lucky twice in a row and got an opportunity to set up and get an attack off.

Maybe if that buff was more like a 20% bump up to 50% (which I still don't see happening), with it's HP and Defense stat's it could easily set up a Hone Claws (which it would obviously have with your description) which would just be silly.